Gas Resources of the Montana Thrust Belt

Hansen, William B. ¹ (1) Consulting Geologist, Jireh Consulting Services, Great Falls, MT

The Paleozoic Waterton-Rundle Foothills Play of Alberta extends southward to at least as far south as Helena, Montana. The gas is sourced from the underlying Bakken/Exshaw Formation which is mature and within the gas generating window throughout much of the foothills east of the Lewis Thrust. Sources also exist in the Cretaceous and Mississippian Big Snowy Group. Undiscovered resource estimates for the play range from 8.6 - 12.1 TCF, depending on the methodology used. Obviously, the Montana play is still in the frontier exploration stage.

In the early 1980’s gas production was re-established in the Montana Thrust Belt at Blackleaf Canyon Field (Mississippian). This field was originally discovered, shut-in, and abandoned  and 60’s, as exploration migrated southward from giant Waterton Gas Field (4 TCF) in the southern Alberta Foothills.

Unlike its Alberta neighbors, who have found 19 TCF since initial discoveries 60 years ago, Montana Foothills production has barely surpassed 7 BCF, despite its close proximity to existing gas lines. This limited development is due more to “political” barriers than permeability barriers, however. Despite the set backs, a hand full of significant, deep exploratory tests have been drilled on private lands over the last ten years.

The high price of natural gas may finally be pulling some of these “political” barriers down. Even the Helena National Forest has reinstituted oil and gas leasing, albeit with severe restrictions. South of Glacier Park, the U.S. Government is finalizing negotiations for a deep Paleozoic exploratory test on an existing Federal lease in the heart of the play.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana